On-Site Guide (BS 7671_2018) (Electrical Regulations) ( PDFDrive ) (1).pdf

Published by the Institution of Engineering and Technology, London, United Kingdom
The Institution of Engineering and Technology is registered as a Charity in England & Wales
(no. 211014) and Scotland (no. SC038698).
The Institution of Engineering and Technology is the institution
formed by the joining together of the lEE (The Institution of
Electrical Engineers) and the liE (The Institution of Incorporated
Engineers).
© 1992, 1995, 1998, 2002, 2004 The Institution of Electrical Engineers
© 2008, 2011, 2015, 2018 The Institution of Engineering and Technology
First published 1992 (0 85296 537 0)
Reprinted (with amendments) May 1993
Reprinted (with amendments to Appendix 9) July 1993
Reprinted (with amendments) 1994
Revised edition (incorporating Amendment No. 1 to BS 7671:1992) 1995
Reprinted (with new cover) 1996
Revised edition (incorporating Amendment No.2 to BS 7671:1992) 1998
Second edition (incorporating Amendment No. 1 to BS 7671:2001
) 2002 (0 85296 987 2)
Reprinted (with new cover) 2003
Third edition (incorporating Amendment No.2 to BS 7671:2001
) 2004 (0 86341 374 9)
Fourth edition (incorporating BS 7671:2008) 2008 (978-0-86341-854-9)
Reprinted (with amendments) October 2008
Fifth edition (incorporating Amendment No. 1 to BS 7671 :2008) 2011 (978-1-84919-287-3)
Reprinted 2012
Reprinted (with minor corrections) 2013
Reprinted 2014
Sixth edition (incorporating Amendment No.3 to BS 7671:2008) 2015 (978-1-84919-887-5)
Reprinted (with minor corrections) 2015
Seventh Edition (incorporating 18th Edition to BS 7671:201 8) 2018 (978-1-78561-442-2)
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ISBN 978-1-78561-442-2 (wiro bound)
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Cooperating organisations 6
Preface 7
Foreword 9
Section 1 Introduction 11
1.1 Scope 11
1.2 Building Regulations 12
1.3 Basic information required 15
1.4 Intended departures from BS 7671 15
Section 2 The electrical supply 17
2.1 General layout of equipment 17
2.2 Function of components 19
2.3 Separation of gas installation pipework from the electrical installation 23
2.4 Portable generators 24
Section 3 Protection 31
3.1 Types of protective device 31
3.2 Protection against overload current 31
3.3 Protection against short-circuit current and earth fault current 31
3.4 Protection against electric shock 32
3.5 Automatic disconnection 33
3.6 Residual current devices (RCDs) 34
3.7 Surge protective devices (SPDs) 38
3.8 Arc Fault Detection Devices (AFDD) 45
Section 4 Earthing and bonding 47
4.1 Protective earthing 47
4.2 Legal requirements 47
4.3 Main protective bonding 47
4.4 Earthing conductor and main protective bonding conductor
cross-sectional areas 48
4.5 Main protective bonding of plastic services 49
4.6 Supplementary bonding 50
4.7 Additional protection -supplementary equipotential bonding 51
4.8 Supplementary bonding of plastic pipe installations 51
4.9 Earth electrode 51
4.10 Types of earth electrode 51
4.11 Typical earthing arrangements for various types of earthing system 52
On-SiteGuide 3
©The Institution of Engineering andT
echnology

The Institution of Engineering and Technology acknowledges the invaluable contribution
made by the following individuals in the preparation of the On-Site Guide:
Institution of Engineering and Technology
J. Bradley BSc CEng FIET FCIBSE
S. Devine MIET
Eur lng Leon Markwell MSc, BSc(Hons), CEng,
MIET, MCIBSE, LCGI
G.D. Cranshaw CEng FIET G. Gundry MIET
P.E. Donnachie BSc CEng FIET
Special thanks to:
.,.. A Samad Khan MEng (Hons) CEng MIET, MIEEE PEL 37/1, GEL 81
.,.. John Peckham - Stroma Certification
.,.. Bob Cairney - SELECT
We would like to thank the following organisations for their continued support:
British Cables Association
British Electrotechnical &Allied Manufacturers Association Ltd
British Gas
British Standards Institution
Certsure trading as NICEIC and Elecsa
Ministry of Housing, Communities &Local Government
ECA
Electrical Contractors' Association of Scotland t/a SELECT
ENA
NEC Ltd
Revised, compiled and edited
ERATechnology Ltd
ElectricaI Safety First
Health and Safety Executive
IHEEM
NAPIT
The Safety Assessment Federation (SAFed)
UHMA
Society for PublicArchitecture,
Construction, Engineering and Surveying
M. Coles BEng(Hons) MIET, The Institution of Engineering and Technology, 2018
6 On-Site Guide
©The Institution of Engineering and Technology

Section 11 Operation of RCDs 117
11.1 General test procedure 118
11.2 General-purpose RCCBs to BS 4293 118
11.3 General-purpose RCCBs to BS EN 61008 or RCBOs to BS EN 61009 and
BS EN 62423 118
11.4 RCD protected socket-outlets to BS 7288 118
11.5 Additional protection 118
11.6 Integral test device 119
11.7 Multipole RCDs 119
Appendix A Maximum demand and diversity 121
Appendix B Maximum permissible measured earth fault loop
impedance 125
Appendix C Selection of types of cable for particular uses and
external influences 133
Appendix D Methods of support for cables, conductors and
wiring systems 139
Appendix E Cable capacities of conduit and trunking 145
Appendix F Current-carrying capacities and voltage drop for copper
conductors 151
Appendix G Cert.ification and reporting 163
Appendix H Standard circuit arrangements for household and similar
installations 187
Appendix I Resistance of copper and aluminium conductors 195
Appendix J Selection of devices for isolation and switching 199
Appendix K Identification of conductors 201
Appendix L Degrees of protection provided by enclosures
(IP code) 207
Index 209
On-Site Guide 5
© The Institution of Engineering andTechnology

The On-Site Guide is one of a number of publications prepared by the lET to provide
guidance on certain aspects of BS 7671 :2018 Requirements for Electrical Installations,
lET Wiring Regulations, 18th Edition. BS 7671 is ajoint publication ofthe British Standards
Institution and the Institution of Engineering and Technology.
110.1 The scope generally follows that of BS 7671 .The Guide includes material not included in
BS 7671, it provides background to the intentions of BS 7671 and gives other sources of
information. However, it does not ensure compliance with BS 7671 . It is a simple guide
to the requirements of BS 7671; electrical installers should always consult BS 7671 to
satisfy themselves of compliance.
It is expected that persons carrying out work in accordance with this guide will be
competent to do so.
HSR25, EWR Electrical installations in the United Kingdom which comply with the lET Wiring
Regulation 16 Regulations, BS 7671, must comply with all relevant statutory regulations, such as the
Electricity at Work Regulations 1989, the Building Regulations and, where relevant, the
Electricity Safety, Quality and Continuity Regulations 2002, as amended.
114.1 It cannot be guaranteed that BS 7671 complies with all relevant statutory regulations.
115.1 It is, therefore, essential to establish which statutory and other appropriate regulations
apply and to install accordingly. For example, an installation in licensed premises may
have requirements which differ from or are additional to those of BS 7671, and these
will take precedence.
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©The Institution of Engineering and T
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8 On-Site Guide
e The Institution of Engineering and Technology

Part 1 This Guide is concerned with limited application of BS 7671 in accordance with paragraph
1.1: Scope.
BS 7671 and the On-Site Guide are not design guides.
It is essential to prepare a design and/or schedule of the work to be done prior to
commencement or alteration of an electrical installation and to provide all necessary
information and operating instructions of any equipment supplied to the user on
completion.
Any specification should set out the detailed design and provide sufficient information to
enable competent persons to carry out the installation and commissioning.
The specification must provide for all the commissioning procedures that will be required
and for the production of any operation and maintenance manual and building logbook.
The persons or organisations who may be concerned in the preparation of the
specification include the:
Ill> Designer(s)
Ill> lnstaller(s)
Ill> Electricity Distributor
Ill> Installation Owner and/or User
Ill> Architect
Ill> Local Building Control Authority/Standards Division or Approved Inspector
Ill> Fire Prevention Officer
Ill> CDM Coordinator
Ill> BIM Coordinator
Ill> Regulatory Authorities
Ill> Licensing Authority (where necessary)
Ill> Health and Safety Executive.
In producing the specification, advice should be sought from the installation owner and/
or user as to the intended use. Often, such as in a speculative building, the detailed
intended use is unknown. In those circumstances the specification and/or the operation
and maintenance manual and building logbook must set out the basis of use for which
the installation is suitable.
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Precise details of each item of equipment should be obtained from the manufacturer
and/or supplier and compliance with appropriate standards confirmed.
The operation and maintenance manual must include a description of how the installed
system is to operate and must include all commissioning records. The manual should also
include manufacturers' technical data for all items of switchgear, luminaires, accessories,
etc. and any special instructions that may be needed.
Building Regulations 2010, Part L 2013 (Amended 2016) of England, for example,
requires that building owners or operators are provided with summary information
relating to a new or refurbished building which includes building services information
and the maintenance requirements in a buildinglogbook. Information on how to develop
and assemble a building logbook can be obtained from CIBSE:
Tel.:
Website:
Address:
020 8675 5211
www.cibse.org
CIBSE
222 Balham High Road
London
SW12 985
The Health and Safety at Work etc. Act 1974 Section 6 and The Construction (Design
and Management) Regulations 2015 are concerned with the provision of information.
Guidance on the preparation of technical manuals is given in BS EN 82079-1:2012
Preparation of instructions for use. Structuring, content and presentation General
principles and detailed requirements and BS 4940 series (1994) Technical information
on construction products and services. The size and complexity of the installation will
dictate the nature and extent of the manual.
10 On-Site Guide
© The Institution of Engineering and Technology

1.1 Scope
This Guide is for installers (for simplicity, the term installer has been used for electricians
and electrical installers). It covers the following installations:
Part 7 Note:
(a) domestic and similar installations, including off-peak supplies, supplies to
associated garages, outbuildings and the like; and
(b) small industrial and commercial single- and three-phase installations.
Special Installations or Locations (Part 7 of BS 7671) are generally excluded from this Guide.
Advice, however, is given on installations in locations containing a bath or shower and
underfloor heating installations.
This Guide is restricted to installations:
313.1 (a) at a supply frequency of 50 Hz
(b) at a nominal voltage of 230 V AC single-phase or 400/230 V AC three-phase
(c) supplied through a distributor's cut-out having a fuse or fuses rated at 100 A or
less to one of the following standards:
- BS 88-2
- BS 88-3
- BS 88-6
- BS 1361 Type II
Note: BS 1361 was withdrawn in March 2010 and replaced by BS 88-3; BS 88-2.2 and BS 88-6 were
withdrawn in March 2010 and replaced by BS 88-2 (BS EN 60269-2) but fuses complying with
these withdrawn standards will be found in existing installations for many years to come.
(d) typical maximum values of earth fault loop impedance, Ze, for TN earthing
arrangements outside the consumer's installation commonly quoted by
distributors are as follows:
ll> TN-C-S arrangement - 0.35 0, see Figure 2.1 (i)
ll> TN-S arrangement - 0.8 0, see Figure 2.1(ii)
Note: The values of 0.35 0 and 0.8 0 are typical maximum values as quoted by distributors of
electricity upon enquiry which will aid, for example, designs for new-build installations.
Table 41.5 For a TT arrangement, 21 0 is the usual stated maximum resistance of the
542.2.4 distributor's earth electrode at the supply transformer. The resistance of the
consumer's installation earth electrode should be as low as practicable and an
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1
earth electrode resistance or Ze measurement exceeding 200 0 may not be
stable due to environmental changes, i.e. drying out in summer and freezing in
winter.
Appx E This Guide also contains information which may be required in general installation work,
for example, conduit and trunking capacities, bending radii of cables, etc.
The Guide introduces the use of standard circuits, which are discussed in Section 7.
However, because of simplification, this Guide may not give the most economical result.
This Guide is not a replacement for BS 7671, which should always be consulted.
Defined terms according to Part 2 of BS 7671 are used.
In compliance with the definitions of BS 7671, throughout this Guide the term line
conductor is used instead of phase conductorand live part is used to refer to aconductor
or conductive part intended to be energised in normal use, includinga neutral conductor.
The terminals of electrical equipment are identified by the letters L, N and E(or PE).
Further information is available in the series of Guidance Notes published by the lET:
Ill> GN 1 Selection &Erection
Ill> GN 2 Isolation & Switching
Ill> GN 3 Inspection &Testing
Ill> GN 4 Protection Against Fire
Ill> GN 5 Protection Against Electric Shock
Ill> GN 6 Protection Against Overcurrent
Ill> GN 7 Special Locations
Ill> GN 8 Earthing &Bonding
Notes:
For clarification:
.,. the distributor of electricity is deemed to be the organisation owning or operating the electrical
supply equipment, and
.,. the supplier of electricity is the organisation from whom electricity is purchased.
1.2 Building Regulations
Refer to the lET publication Electrician's Guide to the Building Regulations for more in-
depth guidance on electrical installations in dwellings.
1.2.1 England - The Building Regulations 2010
Persons carrying out electrical work in dwellings must comply with the Building
Regulations of England, in particular Part P (Electrical safety - dwellings).
Persons responsible for work within the scope of Part Pof the Building Regulations may
also be responsible for ensuring compliance with other Parts of the Building Regulations,
where relevant, particularly if there are no other parties involved with the work. Building
Regulations requirements relevant to installers carrying out electrical work include:
12 On-Site Guide

1
1.2.2 The Building (Scotland) Regulations 2004 (as
amended)
The detailed requirements are given in the Technical Standards for compliance with the
Building (Scotland) Regulations.
Guidance on how to achieve compliance with these Standards is given in two Scottish
Building Standards Technical Handbooks- Domestic and Non-domestic.
These handbooks contain recommendations for electrical installations, including the
following:
- compliance with BS 7671
- minimum number of socket-outlets in dwellings
- minimum number of lighting points in dwellings
- minimum illumination levels in common areas of domestic buildings, for
example, blocks of flats
- a range of mounting heights of switches and socket-outlets, etc.
- separate switching for concealed socket-outlets, for example, behind white
goods in kitchens
- conservation of fuel and power in buildings.
With regard to electrical installations in Scotland, the requirements of the above are
deemed to be satisfied by complying with BS 7671.
Note: The handbooks are available in electronic format only from the Building Standards Division of
the Scottish Government from website: www.scotland.gov.uk/bsd
1.2.3 The Building Regulations of Northern Ireland
The Building Regulations (Northern Ireland) 2000 (as amended) apply.
Note: Information can be obtained from the website: www.buildingcontrol-ni.com
1.2.4 The Building Regulations of Wales
On 31 December 2011 the power to make building regulations for Wales was transferred
to Welsh Ministers. This means Welsh Ministers will make any new building regulations
or publish any new building regulations guidance applicable in Wales from that date.
The Building Regulations 2010 and related guidance for England and Wales, including
approved documents as at that date, will continue to apply in Wales until Welsh Ministers
make changes to them. As guidance is reviewed and changes made, Welsh Ministers will
publish separate approved documents.
14 On-Site Guide

1
313.1 1.3 Basic information required
544.1
312
Before starting work on an installation which requires a new electrical supply, the installer
should establish the following information with the local electricity distributor:
(a) the number of live conductors required by the design
(b) the distributor's requirement for cross-sectional area and maximum* length of
the consumer's tails
(c) the maximum prospective fault current (lpf) at the supply terminals
(d) the typical maximum earth fault loop impedance (Ze) of the earth fault path
outside the consumer's installation
(e) the type and rating of the distributor's fusible cut-out or protective device
(f) the distributor's requirements regarding the size of main protective bonding
conductors
(g) the conductor arrangement and system earthing
(h) the arrangements for the incoming cable and metering.
*Some distributors will specify a maximum permitted length for consumer's tails. The
distributor may also apply particular requirements for isolation or protection.
132.16 For additions and alterations to existing installations, installers should satisfy themselves
as to the suitability of the supply, the distributor's equipment and the earthing and
bonding arrangements.
120.3 1.4 Intended departures from BS 7671
Where the designer decides to depart from the requirements of BS 7671, the resulting
degree of safety must not be less thanthat obtained by compliance with the Regulations.
The designer is responsible for the safety of the design. Any intended departure from
the requirements of BS 7671, although the designer is confident regarding safety, must
be recorded on the Electrical Installation Certificate. There is a difference between an
intended departure and a non-compliance; points to note:
- an intended departure must be recorded on the Electrical Installation
Certificate
- an intended departure not recorded on the Electrical Installation Certificate
is unacceptable, as it is simply a non-compliance and the certificate would,
therefore, be worthless.
On-Site Guide 15

1
16 On-Site Guide

2.1 General layout of equipment
The general layout of the equipment at the service position is shown in Figures 2.1 (i) to
2.1(iii), including typical protective conductor cross-sectional areas.
The following scenarios are considered:
..,._ Figure 2.1 (i) TN-C-S (PME) earthing arrangement
..,._ Figure 2.1 (ii) TN-S earthing arrangement (cable sheath earth)
..,._ Figure 2.1 (iii) TT earthing arrangement (no distributor's earth provided/used)
T Figure 2.1 (i) TN-C-S (PME) earthing arrangement
•·••••41
kWh
consumer's tails
isolator
switch -
~ n
-
•
main switch
circuit protective metal water
conductors pipe
metal gas
pipe
LABEL (see Figure 6.5)
RCBOs
water
service
pipe
/ ~
gas
service
pipe
Note: An electricity isolator switch may not always be installed by the distributor.
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2
T Figure 2.1(ii) TN-S earthing arrangement (cable sheath earth)
isolator
switch
consumer's tails
.
t •I •
main switch
16mm2
conductors pipe
metal gas
pipe
LABEL (54!e Figure6.5)
/
lOmm'
RCBOs
water
lOmm'
gas meter
gas
service
pipe
Note: An electricity isolator switch may not always be installed by the distributor.
T Figure 2.1(iii) n earthing arrangement (no distributor's earth provided/used)
IOOA
conductors pipe
metal gas
pipe
consumer's tails
"
electricity
isolator
switch
RCBOs
main switch
16mm'
LABEL (see Rgure 6.5)
~
earth
decbode
LABEL(see Figure 65)
/
water
service
pipe
IOmm'
gas
service
pipe
gas meter
Note 1: An electricity isolator switch may not always be installed by the distributor.
542.3.1 Note 2: See Table 4.4{ii) for further information regarding the sizing of the earthing conductor for a
TT earthing arrangement.
Note 3: See 2.2.6 for requirements for consumer unit enclosures.
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2.2 Function of components
2.2.1 Distributor's cut-out
2
This will be sealed to prevent the fuse being withdrawn by unauthorised persons. When
the consumer's tails and consumer unit are installed in accordance with the requirements
of the distributor, the cut-out may be assumed to provide protedion against fault current
up to the consumer's main switch.
As the cut-out is the property of the distributor, installers must not cut seals and withdraw
cut-out fuses without permission. Where removal of the cut-out for isolation is required,
the supplier of electricity should be contacted to arrange disconnection and subsequent
reconnection.
Note: The supplier of electricity may not be the same organisation as the distributor; see 1.1.
2.2.2 Eledricity meter
The terminalswill be sealed by the meter owner to prevent interference by unauthorised
persons.
2.2.3 Meter tails
521.10.1 Meter tails fall into two categories, supplier's tails and consumer's tails and there is a
need to differentiate between the two.
T Figure 2.2.3 Meter tails
consumer's tails
RCBOs
• •
supplier's
tails electricity
isolator main switch
-
l OOA
switch
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© The Institution of EngineeringandTechnology

2
2.2.3.1 Consumer'stails
The cables between the electricity meter and the consumer unit, known as the
consumer's tails, are part of the consumer's installation and should be insulated and non-
metallic sheathed or insulated and enclosed within containment, for example, conduit or
trunking. Consumer's tails are provided by the installer and are the responsibility of the
owner of the electrical installation.
514.3.1 Polarity should be indicated by the colour of the insulation and the minimum cable size
should be 25 mm2
• The distributor may specify the maximum length of tails between
the meter and the consumer unit in addition to the minimum cross-sectional area
(see 1.3). In some cases, the distributor may require an electricity isolator switch
(see 2.2.4).
434.3(iv) Where the consumer's tails are protected against fault current by the distributor's cut-out,
the method of installation, maximum length and minimum cross-sectional area of the
tails must comply with the requirements of the distributor.
5226202
5526.203
2.2.3.2 Supplier's tails
The cables between the supplier's cut-out and the electricity meter, known as the
supplier's tails, are part of the supplier's equipment.
Where tails are buried in walls or enclosed within the fabric of the building, further
protection is required (see 7.3.2).
It is important that both supplier's and consumer's tails are sufficiently protected from
mechanical damage and disturbance by the use of trunking and/or cable clips; see 2.2.6
of this Guide.
2.2.4 Eledricity isolator switch
Distributors may provide and install an electricity isolator switch between the meter and
the consumer unit, labelled as Electricity isolator switch in Figures 2.1(i) to 2.1(iii) and
2.2.3. This double-pole switch permits the supply to the installation to be interrupted
without withdrawing the distributor's cut-out fuse.
2.2.5 Consumer's cont.rolgear
536.4.201 A consumer unit assembly (to BS EN 61439-3:2012) is for use on single-phase
installations up to 100 Aand may include the following components:
Jilt- a double-pole isolator
Jilt- fuses, circuit-breakers or RCBOs for protection against overload and fault
currents
Jilt- RCDs for additional protection against electric shock
Jilt- RCDs for fault protection.
Jilt- Arc Fault Detection Devices (AFDD) for additional protection against fire.
Alternatively, a separate main switch and distribution board may be provided.
20 On-Site Guide

421.1.201
421.1.201
531.3.5.3.2.
201
2
All devices and components shall only be those declared suitable according to the
assembly manufacturer's instructions or literature. The scope of BS EN 61439-3 includes
distribution boards with an incoming rated current not exceeding 250 A and outgoing
circuits not exceeding 125 A. They are intended to be operated by ordinary persons.They
can be used in domestic and commercial single and three-phase installations up to 100
Awithin the scope of this guide.
See lET Guidance Note 1 -Selection and Erection and BEAMA guide Overload protection
of an RCCB or switch in an LV assembly to BS EN 61439-3 available at http://www.
beama.org.uk/resource-library.html.
2.2.6 Consumer unit assemblies
Where a consumer unit assembly is installed in domestic (household)
domestic garages and outbuildings, one of the following applies:
.
prem1
ses,
..,. the enclosure is to be manufactured from non-combustible material; or
..,. the consumer unit is enclosed in a cabinet constructed from non-combustible
material.
Ferrous metal, i.e. steel, is deemed to be an example of a non-combustible material.
Plastic enclosures manufactured from 960 degree glow-wire rated material would not be
classified as 'non-combustible' in the context of this regulation.
Where a steel consumer unit is installed in an installation forming part of a n system,
the earth fault loop impedance, 4, is likely to be much higher than the maximum that
is permitted for use of the overcurrent protective device, i.e. cut-out, in order to provide
fault protection. Should the consumer's tails become loose or damaged and make
contact with the metal enclosure, it is likely that the overcurrent device will not operate
within the maximum permitted time of 5 s.
The lET's Wiring Regulations Policy Committee, therefore, advises the following:
(a) AClass I metal consumer unit is installed and each outgoing circuit is protected
by an RCBO
(b) A split, Class I metal consumer unit is installed, where the double-pole main
switch of the consumer unit should incorporate an S type (time delayed)
RCCB, e.g. 100 mA S-type RCCB.
Note: In cases where RCBOs protect each outgoing circuit, the risk of the solid busbar (connecting
the supply side of each RCBO) making contact with the ferrous enclosure is minimal. In
split consumer units, where two or three RCCBs protect multiple circuits through individual
circuit-breakers, the risk of the single-insulated conductors (connecting the load side of the
double-pole main switch to the supply side of the RCCBs) making contact with the ferrous
enclosure due to vibration and/or abrasion or being damaged is far higher. In essence, where
the construction and layout of the consumer unit is such that the risk of live conductors making
contact with the ferrous enclosure is minimal, then the double-pole main switch need not
incorporate an S-type RCCB.
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2
412.2.4.1
531.3.5.3.
2.201
522.8.1
In all cases:
(a) the consumer's tails need to meet the requirements for the protective measure
of double or reinforced insulation throughout their length. This can be achieved
by the use of single-core insulated and non-metallic sheathed cable with the
sheath being kept on the right up to the terminals of the incoming device (main
switch or RCD) of the consumer unit.
(b) the consumer's tails need to be protected to avoid mechanical damage and
disturbance at the incoming terminals in the consumer unit in order to avoid
the line conductor becoming disconnected and making contact with the metal
enclosure. This can be achieved by, for example, clipping or clamping the
consumer's tails, or by installing them in trunking and the use of a suitable
cable-entry gland. In all cable entry arrangements, the enclosure shall not have
sharp edges that could damage cables.
T Figure 2.2.6a Example of clipping tails to arrest movement
Cables clipped at relevant positions circuit protective metal water
to arrest movement ~sumer's tails conductors pipe
metal gas
pipe
LABEL (see Figure 6.5)
electricity
isolator
switch
supplier's tails
- RCBOs
•
main switch
16mm2
lOOA~----------==================?
water
service
pipe
/
gas
service
pipe
(c) The cable installation entry method shall, so far as is reasonably practicable,
maintain the fire containment of the enclosure. It is essential that account be
taken of the manufacturer's instructions, if any.
This can generally xbe achieved by the installer ensuring that cable access
holes they make in the enclosure do not to leave gaps greater than:
• 1.0 mm for the horizontal top surface and
• 2.5 mm for all other surfaces of the enclosure that are accessible after
installation.
22 On-Site Guide

522.8.1
521.5.1
2
The installer could for example, select as they deem appropriate; trunking,
conduit, cable gland or cable entry accessories to minimise the opening around
the cables.
(d) the consumer's tails also need to be protected to avoid any foreseeable damage
and, where entering a ferrous enclosure, do so through the same entry point.
A non-combustible enclosure includes base, cover, door and any components, e.g.
hinges, covers, screws and catches necessary to maintain fire containment. Devices and
blanks are contained within the non-combustible enclosure and, therefore do not have
to be manufactured from a non-combustible material, e.g. steel. However, the use of
non-combustible blanks is not precluded.
Note: Information on consumer units kindly provided by BEAMA. This and more can be found here:
http://www.beama.org.uk/en/publications/technical-bulletins.cfm
Where the consumer unit is to be located in an external non-habitable building, e.g. a
garage or shed, which is not in close proximity to a dwelling, consideration could still be
given to installing a consumer unit of non-ferrous construction. The term "not in close
proximity" is always a moot point and the decision to install a non-ferrous enclosure
must be supported by a documented risk assessment, which must be appended to the
Electrical Installation Certificate.
2.3 Separation of gas installation pipework
from the electrical installation
Where gas installation pipework is not separated from electrical equipment or cables
by an insulating enclosure, dividing barrier, trunking, or conduit, the following separation
distances shall be followed:
(a) at least 150 mm away from electricity supply equipment, such as metering
equipment, main service cut-outs or supplier (main) isolation switches and
distribution boards or consumer units;
(b) at least 25 mm away from electrical switches, sockets and electricity supply
and distribution cables.
The installation pipeworkshall not be positioned in a manner that prevents the operation
of any electrical accessory, i.e. a switch or socket-outlet.
Note: Where these spacing requirements are impracticable the pipework should either be sheathed
with an electric insulating material rated at 230 V or more, or a panel of electrical insulating
material should be interposed.
The cited distances are quoted within BS 6891:2015 Specification for the installation
and maintenance of low pressure gas installation pipework of up to 35 mm (R1114) on
premises, clause 8.4.2.
On-Site Guide 23

2
T Figure 2.3 Separation from the gas installation
'
-I
'~...- Separation of at least 25 mm from switches,
I
I I socket-outlets and supply or distribution cables
- Supply cable or
distribution cable
Minimum
- distance
150mm
Separation of at least 1SO mm from electricity supply equipment,
e.g. metering equipment, main service cut outs or supplier (main)
isolation switches and distribution boards or consumer units
2.4 Portable generators
551.4.4 It is recognised that generators will be used occasionally as a temporary or short-term
means of supplying electricity for use; for example:
ll> on a construction site
.,.. on stalls at a street market
ll> at an external gathering or function attended by the general public, such as a
country show.
Temporary generators can be divided into two classes, i.e. portable and mobile:
ll> portable generators with an electrical output rating of up to 10 kVA are used for
small-scale work for short-term use, i.e. less than one day, and
.,.. mobile generators are those used for longer periods and can be in excess of
10 kVA output.
This Guide considers three scenarios relating to the use of portable generators; see 2.4.1
to 2.4.3.
24 On-Site Guide

2
551 For information relating to the permanent use of generators see lET Guidance Notes 5
and 7 and Section 551 of BS 7671:2018.
551.4.4
413
418.3
Where generators are used to supply concession vehicles, such as burger vans, see
Section 717 Mobile and Transportable Units of BS 7671:2018 and lET Guidance Note 7.
1.4.1 Portable generator isolated from earth
Portable generators ranging in output from 0.2 kVA to 10 kVA single-phase are often
isolated from Earth, i.e. there is no connection between the chassis and/or earth
connection of socket-outlet(s) of the unit and the neutral of the generator winding and
Earth. The ends of the generator winding are brought out to one or more three-pin
socket-outlets which should conform to BS EN 60309-2. The earth socket-tube of the
socket-outlet(s) is usually connected internally to the frame of the generator only; see
Figure 2.4.1.
This arrangement is a form of electrical separation, where basic protection is provided
by basic insulation of live parts or by barriers and enclosures, and fault protection is
provided by simple separation of the separated circuit from other circuits and from Earth.
The requirements for electrical separation can be found in Section 413 of BS 7671
where one item of equipment is supplied and Regulation 418.3 where more than one
item of equipment is supplied by the separated circuit. However, the requirements of
Regulation 418.3 could prove difficult or impracticable to meet in a typical application of
a portable generator.
It is extremely important to note that a portable generator isolated from earth should
only be used to supply equipment in the following permutations:
..,. one or more items of Class II equipment
..,. one item of Class I equipment
..,. one or more items of Class II and one item of Class I equipment.
The supply of only Class II equipment, however, is preferable.
No more than one item of Class I equipment should be supplied at any time as faults can
be presented as voltages and operatives can provide a path for current flowing between
exposed-conductive-parts of faulty electrical equipment.
On-Site Guide 25

2
T Figure 2.4.1 Portable generator used with a floating earth
Generator
~------~-~~--~
~------~-~-*--~
Socket-outlet
with overcurrent
protection
Load
Current-using
equipment
2.4.2 Portable generator used without reference to the
condudive mass of the Earth (floating)
551.4.4 Where more than one item of Class I equipment is to be supplied by a single-phase
portable generator, it is important to ensure that the earth connections of the socket-
outlets at the generator are connected to the neutral of the generator winding in addition
to the chassis or frame of the generator. See Figure 2.4.2.
Such a configuration will provide a return path for any fault current caused by contact
between live parts and exposed-conductive-parts of the connected equipment. Note
that neither of the live conductors of the generator are connected to the conductive
mass of the Earth. If this method of supply is used, extreme care should be taken
to ensure that there is no intended or casual interconnection with any other electrical
system, such as extraneous-conductive-parts or exposed-conductive-parts from other
electrical systems.
R
CDs providing additional protection at 30 rnA are required for all circuits supplied in
this manner.
26 On-Site Guide

BS 7430:
2011+A1:
2015
Table
54.1
543.3.1
T Figure 2.4.2 Generator supplying more than one item of equipment
Generator
Socket-outlets
with overcurrent
protection and RCD
protection at 30 mA
1.4.3 Portable generator referenced to the condudive
mass of the Earth
2
Where there are extraneous-conductive-parts or exposed-conductive-parts of other
electrical systems present, generator reference earthing, by means of an earth electrode
to the conductive mass of the Earth, should be installed. See Figure 2.4.3(i).
Note that this does not create a n system; the system will be TN-Sfrom the generator,
the neutral or star point being referenced to the conductive mass of the Earth.
Where an earth electrode is supplied it will need to be tested by the standard method
using a proprietary earth electrode resistance tester; see 10.3.5.2.
Note that an earth fault loop impedance tester cannot be used for this test as the
earth electrode is not used as a means of earthing, it is used to reference the portable
generator to the conductive mass of the Earth and does not form part of the earth loop.
As the earth electrode is used for referencing and not as a means of earthing, its
resistance should, ideally, be lessthan 200 0.
If buried, generator reference earthing and/or bonding conductors should be sized
in accordance with Table 54.1 and suitably protected in accordance with Regulation
543.3.1. For example, a 16 mm
2
conductor would generally be adequate for short-term
use where no mechanical protection is provided.
On-Site Guide 27

2
T Figure 2.4.3(i) Generator reference earthing - using earth electrode
I
I
Generator
Earth electrode
Socket-outlets
with overcurrent
protection and RCD
protection at 30 rnA
Where restrictions, such as concreted/paved areas or the portable generator is being
used some distance above ground level, make it impossible to install an earth electrode,
simultaneously accessible metal parts, i.e. accessible extraneous-conductive-parts and/
or exposed-conductive-partsfrom other electrical systems, may be bonded to the main
earthing terminal of the generator. See Figure 2.4.3(ii).
544.1.1 Where separate accessible extraneous-conductive-parts and/or exposed-conductive-
parts from other electrical systems are connected together, protective conductors can
be sized in accordance with Regulation 544.1.1. For example, a l6mm2
conductor would
generally be adequate for short-term use where no mechanical protection is provided.
28 On-Site Guide

2
Figure 2.4.3(ii) Generator reference earthing - connection of extraneous-
and/or exposed-conductive-parts where the installation of an
earth electrode is not possible
' ~
:; ,,
:;
:;
:;
.. ~
-
"
'/ ,,
0
Generator
rlll
lJ
•
~~
....
....~:
~,- '-._,
<- p
.. ' ·
... ·?~
...
Socket-outlets
with overcurrent
protection and RCD
l~
protection at 30 mA
'
On-Site Guide 29

2
30 On-Site Guide

433
434
411.3.2
415.1
421.1.7
3.1 Types of protective device
The consumer unit (or distribution board) may contain devices providing:
(a) protection against overload current
(b) protection against short-circuit current and earth fault current
(c) automatic disconnection in case of a fault (fault protection)
(d) additional protection (electric shock protection): RCD(s) 30 mA.
(e) additional protection against fire may also be included (AFDD)
Functions (a) and (b) are usually carried out by one device, i.e. a fuse or circuit-breaker.
434 Function (c) is usually carried out by the device performing function (b), except where
a high value of earth fault loop impedance makes the use of a fuse or circuit-breaker for
function (c) impracticable (such as a TT system), in which case an RCD has to be used.
434 An RCBO, being a unit with a combined circuit-breaker and RCD, will carry out functions
411 (a) to (d).
Appx3 3.2
533.1
Protection against overload current
Protection against overload current will be provided by the use of any of the following
devices:
..,.. fuses to BS 88-2, (BS EN 60269-2) BS 88-3, BS 88-6, BS 1361 and BS 3036
..,.. miniature circuit-breakers to BS 3871-1 types 1, 2 and 3
..,.. circuit-breakers to BS EN 60898 types B, C and D, and
..,.. residual current circuit-breakers with integral overcurrent protection (RCBOs) to
BS EN 61009 series and BS EN 62423.
3.3 Protection against short-circuit current and
earth fault current
When a consumer unit to BS EN 61439-3:2012 or BS 5486: Part 13 or a fuseboard
having fuselinks to BS 88-2 (BS EN 60269-2) or BS 88-6 or BS 1361 is used, then
protection against short-circuit current and earth fault current will be provided by that
particular overcurrent protective device.
Note: For other protective devices the breaking capacity must be adequate for the prospective fault
current at their point of installation.
On-Site Guide 31
echnology

3
3.4 Protection against electric shock
3.4.1 Automatic disconnection of supply
411 Automatic disconnection of supply (ADS
) isthe most the common method of protection
411.1 against electric shock. There are two elements to automatic disconnection of supply,
basic protection and fault protection.
411.2
411.1
416
416.1
416.2
521.10.1
415.1.1
415.1.2
3.4.1.1 Basic protection
Basic protection is the physical barrier between persons/livestock and a live part.
Examples of basic protection are:
..,. electrical insulation
ll> enclosures and barriers.
It follows that single-core non-sheathed insulated conductors must be protected by
conduit or trunking and be terminated within a suitable enclosure.
A 30 rnA RCD may be provided to give additional protection against contact with live
parts but must not be used as primary protection.
411.3 3.4.1.2 Fault protection
411.1
411.3.1.1
411.3.1.2
411.3.2
Fault protection comprises:
..,. protective earthing,
ll> protective equipotential bonding, and
ll> automatic disconnection in case of a fault.
Fault protection works by limiting the magnitude and duration ofvoltages that may appear
under earth fault conditions between simultaneously accessible exposed-conductive-
parts of equipment and between them and extraneous-conductive-parts or earth.
3.4.2 other methods of protedion against eledric shock
410.3.3 In addition to automatic disconnection of supply, BS 7671 recognises other methods of
protection against electric shock.
414 3.4.3 SELV and PELV
414.3
414.4.1
32
SELV
Separated extra-low voltage (SELV) systems:
ll> are supplied from isolated safety sources such as a safety isolating transformer
to BS EN 61558-2-6 orBSEN 61558-2-8
ll> have no live part connected to earth or the protective conductor of another
system
ll> have basic insulation from other SELV and PELV circuits
ll> have double or reinforced insulation or basic insulation plus earthed metallic
screening from LV circuits
On-Site Guide

414.4.4
414.4.1
414.4.5
3
ll> have no exposed-conductive-parts connected to earth or to exposed-
conductive-parts or protective conductors of another circuit.
PELV
Protective extra-low voltage (PELV) systems must meet all the requirements for SELV,
except that the circuits are not electrically separated from earth.
For SELV and PELV systems, basic protection need not be provided if voltages do not
exceed those given in Table 3.4.3.
T Table 3.4.3 SELV and PEL
V basic protection voltage limits
Location SELV and PELV
Dry areas
Immersed equipment
Locations containing a bath or shower,
swimming pools, saunas
Other areas
25 V AC or 60 V DC
Further protection required at all voltages
Further protection required at all voltages
12VAC or 30V DC
411 3.5 Automatic disconnection
3.5.1 Standard circuits
For the standard final circuits given in Section 7 of this Guide, the correct disconnection
time is obtained for the protective devices by limiting the maximum circuit lengths.
Table 41.1 3.5.2 Disconnection times -TN systems
411.3.2.2 A disconnection time of not more than 0.4 s is required for final circuits:
ll> 63 A with one or more socket-outlets
ll> 32 A when supplying only fixed equipment
411.3.2.3 A disconnection time of not more than 5 s is permitted for:
ll> final circuits exceeding 32 A, and
ll> distribution circuits.
Table 41.1 3.5.3 Disconnection times- TT systems
411.3.2.2 The required disconnection times for installations forming part of a TT system can,
except in the most exceptional circumstances outside the scope of this Guide, only be
achieved by protecting every circuit with an RCD, hence, a time of not more than 0.2 s
is required for final circuits:
ll> 63 A with one or more socket-outlets
ll> 32 A when supplying only fixed equipment.
On-Site Guide 33
©The Institution of Engineering andTechnology

3
411.3.2.4 A disconnection time of not more than 1 s is permitted for:
111> final circuits exceeding 32 A, and
411.4
411.5
411.3.3
(i)
411.3.4
701.411.
3.3
701.411.
3.3
411.3.3
(ii)
522.6.
202
522.6.
203
111> distribution circuits.
3.6 Residual current devices (RCDs)
RCD is the generic term for a device that operates when the residual current in the circuit
reaches a predetermined value. The RCD is, therefore, the main component in an RCCB
(residual current operated circuit-breaker without integral overcurrent protection) or
one of the functions of an RCBO (residual current operated circuit-breaker with integral
overcurrent protection).
3.6.1 Protedion by RCDs
R
CDs are required for:
(a) fault protection where the earth fault loop impedance is too high to meet
the required disconnection time, for example, where the distributor does not
provide a connection to a means of earthing, i.e. TT earthing arrangement
(b) additional protection for socket-outlets not exceeding 32 A
(c) additional protection for lighting circuits in domestic (household) premises
(d) additional protection for all low voltage circuits serving locations containing a
bath or shower
(e) additional protection for all low voltage circuits passing through zones 1 and 2
of locations containing a bath or shower but not serving equipment within the
location
(f) additional protection for circuits supplying mobile equipment not exceeding 32
Afor use outdoors
(g) additional protection for cables without earthed metallic covering installed in
walls or partitions at a depth of less than 50 mm and not protected by earthed
steel conduit, earthed trunking or earthed ducting
(h) additional protection for cables without earthed metallic covering installed in
walls or partitions with metal parts (not including screws or nails) and not
protected by earthed steel conduit or the like.
3.6.2 Omission of RCD protedion
411.3.3 3.6.2.1 Specific cases
411.4
411.5
34
RCDs for additional requirements for socket-outlets can be omitted in non-domestic
premises, where a documented risk assessment determines that RCD protection is not
necessary. The risk assessment must be appended to the certificate issued for the work.
See 3.6.2.2.
Cables installed on the surface do not specifically require RCD protection; however, RCD
protection may be required for other reasons, for example, for fault protection where the
earth fault loop impedance is such that the disconnection time for an overcurrent device
cannot be met.
On-Site Guide

3
411.3.3 3.6.2.2 Risk assessment and the omission of additional requirements by RCDs for
socket-outlets
In non-domestic premises, BS 7671:2018 permits RCDs, where usually provided
for additional protection to socket-outlets, to be omitted where a documented risk
assessment determines that the risk to users and those in the vicinity is sufficiently low
and, hence, RCD protection is not necessary.
411.3.3 The Management of Health and Safety at Work Regulations 1999 puts the responsibility
Note 2 for carrying out risk assessments onto (as applicable) the persons responsible for the
operations or work activity. The risk assessment should consider the frequency of use,
the environment, the equipment to be connected, the skill level of the person using the
equipment and the socket-outlet and the persons who will have access to the area when
the equipment is in operation, amongst many other factors.
The intention is that the omission of RCDs for additional protection to socket-outlets
should be only as a last resort and certainly notfor implementation in domesticpremises.
Note that the risk assessment, like all risk assessments, will need to be revisited at
pertinent intervals to assess any change in circumstances, i.e. change of use/change of
ownership or when a periodic inspection is undertaken and must be appended to the
Electrical Installation Certificate EICR.
3.6.3 Applications of RCDs
314 Installations are required to be divided into circuits to avoid hazards and minimize
inconvenience in the event of a fault and to take account of danger that might arise from
the failure of a single circuit, such as a lighting circuit.
The following scenarios show different methods of providing RCD protection within
installations. Note that, for clarity, earthing and bonding connections are not shown.
On-Site Guide 35

3
3.6.3.1 Examples of RCDs within installations
In each case, refer to 2.2.6 of this Guide.
T Figure 3.6.3(i) Consumer unit with RCBOs, suitable for all installations
(TN and TT)
final circuits
• •
•
.. •
30mARCBOs
labelled main switch
'Main switch' (isolator)
Single RCBOs protect each outgoing circuit and the risk of the busbar (connecting
the supply side of each RCBO) becoming loose and making contact with the ferrous
enclosure is minimal. The use of RCBOs will minimize inconvenience in the event of a
fault and is applicable to all systems.
T Figure 3.6.3(ii) Split consumer unit with separate main switch and two 30 rnA
RCCBs
final circuits final circuits
• • • •
main switch 30 mA 30 mA
(isolator) RCCB RCCB
labelled
'Main switch'
36 On-Site Guide

3
The division of an installation into two parts with separate 30 mA RCCBs will ensure
that part of the installation will remain on supply in the event of a fault. Generally, this
is not suitable for an installation forming part of a TT system as there is insufficient fault
protection of the single insulated conductors which connect the load side of the double-
pole main switch to the supply side of the RCCBs.
'Y Figure 3.6.3(iii) Three-way split consumer unit with separate main switch, two
30 mA RCCBs and circuits without RCD protection
ltllltj•
kWh
specifically labelled circuits
e.g. fire alarms,
medical equipment
final circuits
main switch
(isolator)
labelled
'Main switch'
30mA
RCCB
final circuits
30mA
RCCB
The three-way division of an installation can provide ways unprotected by RCDs for, say,
fire systems and for two separate 30 mA R
CCBs to ensure that part of the installation
will remain on supply in the event of a fault. Unprotected circuits will usually need to be
installed in earthed metal conduit or wired with earthed metal-sheathed cables. This is
not suitable for an installation forming part of a TT system as there is insufficient fault
protection of the single insulated conductors which connect the load side of the double-
pole main switch to the supply side of the RCCBs.
3.6.3.2 RCBOs
The use of RCBOs will minimize inconvenience in the event of a fault and is applicable
to all systems. See Figure 3.6.3(i).
Such a consumer unit arrangement also easily allows individual circuits, such as to
specifically labelled socket-outlets or fire alarms, to be protected by a circuit-breaker
without RCD protection. Such circuits will usually need to be installed in earthed metal
conduit or wired with earthed metal-sheathed cables.
On-Site Guide 37

3
3.6.3.3 Split board with two 30 rnA RCDs
The division of an installation into two parts with separate 30 rnA RCCBs will ensure that
part of the installation will remain on supply in the event of a fault, see Figure 3.6.3(ii).
3.6.3.4 Three-way split board with two 30 rnA RCDs
The three-way division of an installation can provide ways unprotected by RCDs for, say,
fire systems and for two separate 30 rnA RCCBs to ensure that part of the installation
will remain on supply in the event of a fault. Unprotected circuits will usually need to
be installed in earthed metal conduit or wired with earthed metal-sheathed cables, see
Figure 3.6.3(iii).
534 3.7 Surge protective devices (SPDs)
3.7.1 Overview
131.6.2 Electrical installations and connected equipment can be severely affected by lightning
activity during thunderstorms or from electrical switching events.
GN 1 For more information, see lET Guidance Note 1.
443.6.2 Damage can occur when the surge or transient overvoltage, as the result of lightning or
Table electrical switching, exceeds the impulse withstand voltage rating of electrical equipment
443.2 - the levels of which are defined in Table 443.2 of BS 7671:2018.
443
534
Surges from electrical switching events are created when large inductive loads, such as
motors or air conditioning units, switch off and release stored energy which dissipates as
a transient overvoltage. Switching surges are, in general, not as severe as lightning surges
but are more repetitive and can reduce equipment lifespan.
Overvoltages of atmospheric origin, i.e. created by lightning events, in particular, can
present a risk of fire and electric shock owing to a dangerous flashover.
.,. Section 443 of BS 7671:2018 has requirements for the protection of persons,
livestock and propertyfrom injury and damage as aconsequence of overvoltage
.,. Section 534 has requirements for the selection and installation of surge
protective devices.
Note: Section 534 applies to AC power circuits only. When the need for power SPDs is identified,
additional SPDs on other services such as telecommunications lines and equipment is also
recommended. See BS EN 62305 and BS EN 61643.
Note: Some electronic equipment may have protection levels lower than Category I of Table 443.2.
Note: BS 7671:2018 does not specify requirements for protection against transient overvoltages
due to direct or nearby lightning strokes on the structure. For risk management for protection
against transient overvoltages due to direct or nearby lightning strokes on the structure, see BS
EN 62305-2.
38 On-Site Guide

3
3.7.2 Arrangements for protedion against overvoltages
443 Protection according to Section 443 can only be achieved if transient overvoltages are
534 limited to values lower than those given in Table 443.2, requiring the correct selection
and installation of suitable SPDs.
443.1
Table 443.2
443.4
443.4
3.7.2.1 Where SPD protection may not be required
Protection against overvoltages of atmospheric origin is not required in the following
circumstance but the rated impulse withstand voltage of equipment must meet the
requirements of Table 443.2 of BS 7671:2018:
ll> for single dwelling units where the total value of the installation and equipment
therein, does not justify such protection and the consequential losses are
tolerable.
3.7.2.2 Where SPD protection is required
Protection against transient overvoltages shall be provided where the consequence
caused by overvoltage:
(a) results in serious injury to, or loss of, human life, (e.g. hospitals, care homes,
home dialysis equipment)
(b) results in interruption of public services and/or damage to cultural heritage,
(e.g. data centres, heritage status buildings like museums and castles)
(c) results in interruption of commercial or industrial activity (e.g. banks, hotels,
supermarkets, industrial plants, farms)
(d) affects a large number of collocated individuals (e.g. offices, universities,
schools, residential tower blocks)
For all other cases than above a risk assessment to determine the Calculated Risk
Level CRL shall be conducted to 443.5 (see Appendix lET Guidance Note 1 for further
information).
Note: BS EN 62305·2 Protection against lightning risk assessment method must be used for high
risk installations such as nuclear or chemical sites where the consequences of transient
overvoltages could lead to explosions, harmful chemical or radioactive emissions thus
affecting the environment.
The flow chart in Figure 3.7.2.2 will aid the decision-making process for electrical
installations within the scopeof thisGuide.See lET Guidance Note 1formore information.
On-Site Guide 39

-
Q
@0
-t::l
::rv-,
~ - ·
--
::::J (1)
;:!:. C)
C:c::
:::::r. _,
oa..
::::Jro
Q..
g'
<>:9.
~
::::! .
~
"'
5.
~
:::r
::::J
!2.
~
'Y Figure 3.7.2.2 SPD decision flow chart for installations within the scope of this Guide
START
Olrtct Of ntarbylightning strikeson the structtxe;or
structures withrisk of explosion;or where the damage may
alsolrwofw the envlrorvnent(e.g. chemic:illorriitcioactivej
(443.1.1)
NO~
Consequ~es caused
by o~Jerwltage teadsto:
a) se<louslnjvry 100< loss ofhuman !We
b) lnlerrupllon ofpublic services and/ordamage
to cultural heritage
c) Interruptionofcommercial or industrial activity
d) Interruption to an Installation with a large
number ofcollocaled Individuals
(443A)
NO~
Consequences caused by overYOitage for a
single dwelling unitwhere an assessment
shows the tOUII value of theelectrlcal
Installation and connected equipment
d~s norne<essltate the cost of SPO
protection
(443A)
NO~
Consequences caused
by 011ervoltage leads 1D Interruption to oil other
lnstalatlons than detailed above
(443A)
YES
~
....
YES
~
....
YES
~
....
YES
~
....
R.!for to BSEN 62305 fO< rl!k
management to determine
specific protectionagainst

owrvotagerequirtments )
(443.1.1)
_~------
Protectionagainst011ervoltages required- selectedand installedtoSection 534
Where the strudu"' Isequipped with an extemlll ightring protection system LPS 0<
protection against theeffects ofdirect ightnlng on ovorhead lines Type I SPDs shal be
Installedas dose as possible to tho or'lgln ofthe <lectr1clll lnstalatlon. (534.4.13)
Where the structure Is not equipped with an external LPS or does not require protection
against theeffects ofdirect lightning,Typo 2 SPDsshall be Installed ascloseas possible to
theorigin of the electrical Installation. (534.4.1 A)
SPDs Installed closeto sensitiveequipment to further protect against switching transients
originating within the building sl>oll beTypo 2 ortype 3. (534.4.1.1)
(Nole: SPDs can be combined Type SPDs e.g. Tl+2, Tl+2+3, T2+3 -see Appendix 16of _j
85 7671:2018)
'--
(
Prote-ction againstovei''Oitages not
required Ifequipment complies with
required rated Impulse voltage
(Tablo443l)
PerfOfm risk assessment
to determine Calculated
Risk Level CRL value
(443.5)
YES
CRt value k >1000
CRL ~ 1000orif no risk
assessmentIs performed
YES
Check Ifdata, signal and telecom lines require
protection to preserve Lightning Protection
Zones LPZ concept (443.1.1, 534.1, 534.4.1.2)
END
l.N

534.1
534.4
3
3.7.3 Types of SPD protedion
For the protection of AC power circuits, SPDs are allocated a type number:
Ji> Type 1 SPDs are only used where there is a risk of direct lightning current and,
typically, are installed at the origin of the installation
Ji> Type 2 SPDs are used at distribution boards
Ji> Type 3 SPDs are used near terminal equipment.
See also Table 3.7.3.
Appendix Combined Type SPDs are classified with more than one Type, e.g. Type 1 & 2, Type 2
16 & 3, and can provide both lightning current with overvoltage protection in addition to
protection between all conductor combinations (or modes of protection) within a single
unit. Combined Type SPDs provide high surge current handling combined with better
overvoltage protection levels (Up) - the latter being a performance parameter of an SPD.
T Table 3.7.3 CSA of conductors and types of SPD protection
534.4.10
534.4.10
Type Name Location CSA conductor Hazard
1 Equipotential Origin of the 16 mm
2
minimum - Protect against
bonding or installation length of tails - ideally flashover from direct
lightning <0.5 m but no longer lightning strikes to
protection/ than 1m structure orto LV
current SPD overhead supply
2 <Mrvoltage Origin ofthe
2
6 mm or equal Protect against
SPD installation to CSA of circuit overvoltages which can
conductoiS overstress the electrical
installation
T CSA of conductors connecting SPDs and the OCPDs to live conductors
1
2
Type Location CSA conductor
Origin of the installation
Origin of the installation
16 mm
2
minimum - length of tails - ideally <O.S m
but no longer than 1m
6 mm
2
or equal to CSA of circuit conductoiS
3.7.4 Coordination and seledion of surge protedion
Where a number of SPDs are required to operate in conjunction with each other they
must be coordinated to ensurethe correct type of protection is installed where required;
see Figure 3.7.4.
SPD protection should be coordinated as follows:
Ji> choose the correct type of SPD for the installation and site in the correct
location
Ji> refer to Regulation 443.6.2 and Table 443.2 of BS 7671 (impulse withstand
voltage)
On-Site Guide 41

3
534.4.4.2 Ill> choose SPDs with a protection level (Up) sufficiently lower than the impulse
withstand voltage or lower than the impulse immunity of the equipment to be
protected
Ill> choose SPDs of the same make or manufacture.
Note: Coordinated SPDs must be of the same make or manufacture unless the designer is satisfied
that devices of different makes will coordinate as required.
..- Figure 3.7.4 Typical location of a coordinated set of SPDs
Type3
Overvoltage SPD
Terminal equipment
1
42 On-Site Guide
Type2
Overvoltage SPD
Distribution board or
consumer unit
©TheInstitution of Engineering and Technology
Type 1
Equipotential
bonding or lightning
protection/current SPD
Origin

534.4.8
3
3.7.5 Critical length of connecting condudors for SPDs
To gain maximum protection the connecting conductors to SPDs must be kept as short
as possible, to minimize additive inductive voltage drops across the conductors. The total
lead length (a + b) should preferably not exceed 0.5 m but in no case exceed 1.0 m;
see Figure 3.7.5.
Refer to the SPD manufacturer's instructions for optimal installation.
T Figure 3.7.5 Critical length of connecting conductors for SPDs
OCPD
a
r--~ - ... •••• .
SPD VI
..._r""""' • • • • • ••• '
b
Main earthing terminal or
..L, connecting conductor bar
-
OCPD = overcurrent protective device
SPD =surge protective device
E/1 = equipment or installation to be protected against overvoltages
On-Site Guide 43

3
3.7.6 Methods of connection
534.4.3 Primarily, the installation of SPDs must follow the manufacturer's instructions but
minimum SPD connections at the origin of the electrical supply are usually made as
those shown in Figure 3.7.6(i) (TN-C-S, TN-S, TI) and Figure 3.7.6(ii) (TI - SPDs
upstream of RCD):
Type 1 SPDs should be installed upstream from any RCD to avoid unwanted tripping.
Where this cannot be avoided, the RCD should be of the time-delayed or S-type.
534.4.7 T Figure 3.7.6(i) SPDs on load side of RCD
OCPD 1
L1
L2
r i:::::JI RCD I --1--l--.----f=~===f==l
1- L3
N
Protective
conductor _._.
OCPD 2
I --- 1- -
I SPC SPC SPC
I
I I
I I
---- ----
-
-
44 On-SiteG
uide
'
-
-

3
5 T Figure 3.7.6(ii) SPDs on supply side of RCD
34.4.7
OCPD1
L1
L2
- L3
RCD
t
•
N
Protective
OCPD2
conductor
,..- -~
- - - I
I
I SPC SPD SPD
I I
I I I
I I
I
"'= ~~
I
I I
-----------
~ ~ ~ >.J
~ ~
- -
- -
Note: See Appendix 16 of BS 7671:2018 for further information regarding the connection of SPDs.
421.1.7 3.8 Arc Fault Detection Devices (AFDD)
537.6 The use of AFDDs is recommended as additional protection against fire in AC final
circuits. Such protection is not offered by circuit-breakers, fuses and RCDs as AFDDs are
designed to detect low level hazardous arcing that circuit breakers, fuses and RCDs are
not designed to detect. AFDDs detect series and parallel arcs which, for instance, can
occur within damaged cables and loose connections.
AFDDs may be provide as :
(a) one single device, comprising an AFD unit and opening means and intended to
be connected in series with a suitable short circuit protective device declared
by the manufacturer complying with one or more of the following standards
BS EN 60898-1, BS EN 61009-1 orBS EN 60269 series.
(b) one single device, comprising an AFD unit integrated in a protective device
complying with one or more of the following standards BS EN 60898-1, BS EN
61008-1, BS EN 61009-1 orBS EN 62423.
(c) an AFD unit (add-on module) and a declared protective device, intended to
be assembled on site.
AFDDs shall be installed at the origin of the circuit to be protected.
On-Site Guide 45
© The Institution of EngineeringandTechnology

3
46 On-Site Guide

4.1 Protective earthing
The purpose of protective earthing is to ensure that, in the event of a fault, such as
between a line conductorand an exposed-conductive-part or circuit protective conductor,
sufficient current flows to operate the protective device, i.e. fuse to blow, circuit-breaker
to operate or RCD to operate, in the required time.
411.4.2 Every exposed-conductive-part (a conductive part of equipment that can be touched
411.5.1 and which is not a live part but which may become live under fault conditions) shall
be connected by a protective conductor to the main earthing terminal and, hence, the
means of earthing for the installation.
ESQCR
512665
ESQCR (NI)
2012
No. 381
4.2 Legal requirements
ESQCR requires that a distributor of electricity makes the supply neutral conductor or
protective conductor available for the connection of the consumer's protective conductor
where it can be reasonably concluded that such a connection is appropriate. Such a
connection may be deemed inappropriate where there is a risk of the loss of the PEN
conductor, for example, where bare overhead low voltage distribution cables supply a
rural building. In such cases, an installation earth electrode must be provided and the
installation will then form part of a TT system.
Essentially, permission to connect the consumer's protective conductor to the
distributor's neutral can be denied to new installations but, where permission is granted,
the distributor has a responsibility to maintain the connection.
Note: For some rural installations supplied by a PME arrangement, it may be pertinent to install an
additional earth electrode to mitigate the effects of a PEN conductor becoming open-circuit;
see lET Guidance Note 5.
4.3 Main protedive bonding
(Figures 2.1(i) to 2.1(iii))
The purpose of protective bonding is to reduce the voltages between the various
exposed-conductive-parts and extraneous-conductive-parts of an installation, during a
fault to earth and in the event of a fault on the distributor's network.
On-Site Guide 47
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4
411.3.1.2 Main protective bonding conductors are required to connect extraneous-conductive-
Part 2 parts to the main earthing terminal of the installation. An extraneous-conductive-part
is a conductive part, such as a metal pipe, liable to introduce earth potential into the
installation or building. It is common, particularly under certain fault conditions on the
LV supply network, for a potential to exist between true earth, i.e. the conductive mass
of the Earth and the earth of the electrical system. Therefore, buried metallic parts that
enter the building are to be connected to the main earthing terminal of the electrical
installation.
542.3
543.1
Table
54.8
544.1.1
Table
54.8
Examples of extraneous-conductive-parts are:
(a) metallic installation pipes
(b) metallic gas installation pipes
(c) other installation pipework, for example, heating oil
(d) exposed structural steelwork of the building where rising from the ground
(e) lightning protection systems (where required by BSEN 62305).
However, metallic pipes entering the building having an insulating section at their point
of entry need not be connected to the main earthing terminal.
Any internal metallic pipework that may have been buried inthe ground for convenience,
for example, central heating pipeworkcast into the concrete or buried in the floor screed
of a floor at ground level, would normally be considered to be extraneous-conductive-
parts and should be connected to the main earthing terminal.
4.4 Earthing conductor and main protective
bonding condudor cross-sectional areas
The minimum cross-sectional areas (csa) required for the earthing conductor and main
protective bonding conductors are given in Table 4.4(i) and (ii). For TT supplies, refer
to Table 4.4(iii).
T Table 4.4(i) Earthing conductor and main protective bonding conductor sizes
(copper equivalent) for TN-S suplies
CSA Line Conductor mml 6 10 16 25 35 50 70
CSA Earthlnt Conductor 6 10 16 16 16 25 35
CSA Protective Bonding Conductor 6 6 10 10 10 16 25
T Table 4.4(ii) Earthing conductor and main protective bonding conductor sizes
(copper equivalent) for PME (TN-C-S) suplies
CSA Line Conductor mm2 6 10 16 25 35 50 70
CSA Earthlnt Conductor 10 10 16 16 16 25 35
CSA Protective Bonding Conductor 10 10 10 10 10 16 25
48 On-Site Guide

4
Notes:
543.2.4 1 Protective conductors (including earthing and bonding conductors) of 10 mm
2
cross-sectional area
or less shall be copper.
Table 54.7 2 The distributor may require a minimum size of earthing conductor at the origin of the supply of 16
mm
2
copper or greater for TN-Sand TN-C-Ssupplies.
542.3.1 3
Table 54.1
Buried earthing conductors must be at least:
• 25 mm
2
copper if not protected against corrosion
• 50 mm
2
steel if not protected against corrosion
544.1.1
• 16 mm
2
copper if not protected against mechanical damage but protected against corrosion
4
• 16 mm
2
coated steel if not protected against mechanical damage but protected against corrosion.
The distributor should be consulted when in doubt.
'Y Table 4.4(iii) Copper earthing conductor cross-sectional area (csa) for TT supplies
Buried Not buried
Unprotected Protected Protected Unprotected Protected Protected
against against against against
. . .
corros1on corros1on corros1on corros1on
and and
mechanical mechanical
damage damage
2 2 2 2 2 2
mm mm mm mm mm mm
25 16 2.5 4 4 2.5
Notes:
1 Assuming protected against corrosion by a sheath.
2 The main protective bonding conductors shall have a cross-sectional area of not less than half that
required for the earthing conductor and not less than 6 mm
2
.
Note that:
543.2.4 (a) only copper conductors should be used; copper covered aluminium
conductors or aluminium conductors or structural steel can only be used if
special precautions outside the scope of this Guide are taken
544.1.2 (b) where practicable, protective bonding connections to the gas, water, oil, etc.,
service should be within 600 mm of the service meter, or at the point of entry
to the building if the service meter is external and must be on the consumer's
side before any branch pipework and after any insulating section in the service.
The connection must be made to hard pipework, not to soft or flexible meter
connections
542.3.2 (c) the connection must be made using clamps (to BS 951) and be suitably
protected against corrosion at the point of contact.
4.5 Main protedive bonding of plastic services
There is no requirement to main bond an incoming service where the incoming service
pipe is plastic, for example, where yellow is used for natural gas and blue for potable
water.
On-SiteGuide 49

4
Where there is a plastic incoming service and a metal installation within the premises,
main bonding is recommended unless it has been confirmed that any metallic pipework
within the building is not introducing Earth potential (see 4.3).
411.3.1.2 Metallic pipes entering the building and having an insulating section;
- of no less than 100 mm in length, and
544.2
544.2.3
- within 300 mm of the point of entry
need not be connected to the protective equipotential bonding.
4.6 Supplementary bonding
The purpose of supplementary bonding is to reduce the voltage between the various
exposed-conductive-parts and extraneous-conductive-parts of a location during a fault
to earth.
Note: Where a required disconnection time cannot be achieved, supplementary bonding must
be applied, however, this is outside the scope of this Guide. See Regulation 411.3.2.5 and
Guidance Note l.
The cross-sectional area required for supplementary bonding conductors is given in
Table 4.6.
T Table 4 .6 Supplementary bonding conductors
*
Size of
circuit
protective
conductor
2
(mm)
1.0
1.5
2.5
4.0
6.0
10.0
16.0
Minimum cross-sectional area of supplementary bonding conductor (mm
2
)
Exposed-conductive-part
to extraneous-
conductive-part
mechanically
protected
1
1.0
1.0
1.5
2.5
4.0
6.0
10.0
not
mechanically
protected
4.0
4.0
4.0
4.0
4.0
6.0
10.0
Exposed-conductive-
part to exposed-
conductive-part
mechanically
protected
1.0
1.5
2.5
4.0
6.0
10.0
16.0
not
mechanically
protected
4.0
4.0
4.0
4.0
6.0
10.0
16.0
Extraneous-conductive
-part to extraneous-
conductive-part*
mechanically
protected
5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
not
mechanically
protected
4.0
4.0
4.0
4.0
4.0
4.0
4.0
If one of the extraneous-conductive-parts is connected to an exposed-conductive-
part, the bonding conductor must be no smaller than that required by column 1 or 2.
50 On-Site Guide

4.7 Additional protection- supplementary
equipotential bonding
4
415.2 Supplementary equipotential bonding is required in some of the locations and
installations falling within the scope of Part 7 of BS 7671.
If the installation meets the requirements of BS 7671:2018 for earthing and bonding,
there is no specific requirement for supplementary equipotential bonding of:
.,.. kitchen pipes, sinks or draining boards
.,.. metallic boiler pipework
.,.. metallic furniture in kitchens
.,.. metallic pipes to wash-hand basins and WCs
701.415.2 .,.. locations containing a bath or shower, providing the conditions of Regulation
701.415.2 are met.
Note: Metallic waste pipes deemed to be extraneous-conductive-parts must be connected by main
protective bonding conductors to the main earthing terminal; see also 4.3.
4.8 Supplementary bonding of plastic pipe
installations
Supplementary bonding is not required to metallic parts supplied by plastic pipes, for
example, radiators, kitchen sinks or bathroom taps.
4.9 Earth electrode
542.1.2.3 This is connected to the main earthing terminal by the earthing conductor and provides
part of the earth fault loop path for an installation forming part of a n system; see Figure
2.1 (iii).
Table 41.5 It is recommended that the earth fault loop impedance for an installation forming part of
Note 2 a n system does not exceed 200 0.
542.2.6 Metallic gas orwater utility or other metallic service pipes are not to be used as an earth
electrode, although they must be bonded if they are extraneous-conductive-parts; see
also 4.3.
Note: Regulation 542.2.6 permits the use of privately owned water supply pipework for use as an
earth electrode where precautions are taken against its removal and it has been considered for
such use. This provision will not apply to an installation within a dwelling.
4.10 Types of earth electrode
542.2.3 The following types of earth electrode are recognised:
(a) earth rods or pipes
(b) earth tapes or wires
(c) earth plates
On-Site Guide 51

4
542.2.5
542.2.5
(d) underground structural metalwork embedded in foundations or other
metalwork installed in the foundations
(e) welded metal reinforcement of concrete embedded in the ground (excluding
pre-stressed concrete)
(f) lead sheaths and metal coverings of cables, which must meet all the following
conditions:
(i) adequate precautions to prevent excessive deterioration by corrosion
(ii) the sheath or covering shall be in effective contact with Earth
(iii) the consent of the owner of the cable shall be obtained
(iv) arrangements shall exist for the owner of the electrical installation to
be warned of any proposed change to the cable which might affect its
suitability as an earth electrode.
4.11 Typical earthing arrangements for various
types of earthing system
Figures 2.1(i) to 2.1(iii) show single-phase arrangements but three-phase arrangements
are similar.
Table 54.7 The protective conductor sizes as shown in Figures 2.1(i) to 2.1(iii) refer to copper
Table 54.8 conductors and are related to the supplier's incoming cable, where 25 mm2
supplier's
544.1.1 tails are installed.
542.3.1 For TT systems protected by an RCD with an earth electrode resistance 1ohm or greater,
543.1.3 the earthing conductor size need not exceed 2.5 mm2
if protected against corrosion by
a sheath and if also protected against mechanical damage; otherwise, see Table 4.4(iii).
542.4.2 The earthing bar is sometimes used as the main earthing terminal, however, means
must be provided in an accessible position for disconnecting the earthing conductor to
facilitate measurement of external earth fault loop impedance, Ze·
Note: For TN-S and TN-C-5 installations, advice about the availability of an earthing facility and the
precise arrangements for connection should be obtained from the distributor or supplier.
52 On-Site Guide

462 5.1 Isolation
132.15.201 5.1.1 Requirement
462.3
462.1
537.3.2.3
Means of isolation should be provided:
(a) at the origin of the installation
A main linked switch or circuit-breaker should be provided as a means of
isolation and of interrupting the supply on load.
For single-phase household and similar installations, the main switch may be
operated by unskilled persons, a double-pole device must be used for both TT
and TN systems.
For a three-phase supply to an installation forming part of a TT system, an
isolator must interrupt the line and neutral conductors. In a TN-S or TN-C-S
system only the line conductors need be interrupted.
(b) for every circuit
Other than at the origin of the installation, every circuit or group of circuits
that may have to be isolated without interrupting the supply to other circuits
should be provided with its own isolating device. The device must switch all
live conductors in a TT system and all line conductors in a TN system.
(c) for every item of equipment
(d) for every motor
Every fixed electric motor should be provided with a readily accessible and
easily operated device to switch off the motor and all associated equipment
including any automatic circuit-breaker. The device must be so placed as to
prevent danger.
(e) for every supply.
5.1.2 The switchgear
The position of the contacts of the isolator must either be externally visible or be clearly,
positively and reliably indicated.
The device must be designed or installed to prevent unintentional or inadvertent closure.
537.2.4
Each device used for isolation must be clearly identified by position or durable marking
to indicate the installation or circuit that it isolates.
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©The Institutionof Engineering andT
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5
537.3.2.3
514.1.1
If it is installed remotely from the equipment to be isolated, the device must be capable
of being secured in the OPEN position.
Guidance on the selection of devices for isolation is given in Appendix J.
464 5.2 Switching off for mechanical maintenance
464.1
464.2
537.3.2.2
537.3.2.2
537.3.2.3
537.3.2.3
337.3.2.4
464.2
537.3.2.4
537.3.2.2
A means of switching off for mechanical maintenance is required where mechanical
maintenance may involve a risk of injury - for example, from mechanical movement of
machinery or hot items when replacing lamps.
The means of switching off for mechanical maintenance must be able to be made
secureto prevent electrically powered equipment from becoming unintentionally started
during the mechanical maintenance, unless the means of switching off is continuously
under the control of the person performing the maintenance.
Each device for switching off for mechanical maintenance must:
(a) where practicable, be inserted in the main supply circuit
(b) be capable of switching the full load current
(c) be manually operated
(d) have either an externally visible contact gap or a clearly and reliably indicated
OFF position. An indicator light should not be relied upon
(e) be designed and/or installed so as to prevent inadvertent or unintentional
switching on
(f) be installed and durably marked so as to be readily identifiable and convenient
for use.
A plug and socket-outlet or similar device of rating not exceeding 16 A may be used for
switching off for mechanical maintenance.
465 5.3 Emergency switching
465.1
461.2
465.3
537.3.3.3
537.3.3.2
54
An emergency switch is to be provided for any part of an installation where it may be
necessary to control the supply in order to remove an unexpected danger.
Where there is a risk of electric shock the emergency switch is to disconnect all live
conductors, except in three-phase TN-S and TN-C-S systems, where the neutral need
not be switched.
The means of emergency switching must act as directly as possible on the appropriate
supply conductors and the arrangement must be such that one single action only will
interrupt the appropriate supply.
Aplug and socket-outlet or similar device must not be selected as adevice for emergency
switching.
An emergency switch must be:
(a) capable of cutting off the full load current, taking account of stalled motor
currents where appropriate
On-Site Guide

537.3.3.4
537.3.3.5
537.3.3.6
537.3.3.7
537.3.3.6
5
(b) hand operated and directly interrupt the main circuit where practicable
(c) clearly identified, preferably by colour. If a colour is used, this should be red
with a contrasting background
(d) readilyaccessible atthe placewhere dangermightoccurand, where appropriate,
at any additional remote position from which that danger can be removed
(e) of the latching type or capable of being restrained in the 'OFF' or 'STOP'
position, unless both the means of operation and re-energizing are under the
control of the same person. The release of an emergency switching device
must not re-energize the relevant part of the installation; it must be necessary
to take a further action, such as pushing a 'start' button
(f) so placed and durably marked so as to be readily identifiable and convenient
for its intended use.
463 5.4 Functional switching
537.3.1
463.1.1 A switch must be installed in each part of a circuit which may require to be controlled
independently of other parts of the installation.
Switches must not be installed in the neutral conductor alone.
463.1.2
463.1.3 All current-using equipment requiring control shall be controlled by a switch.
537.3.1.1 Off-load isolators, fuses and links must not be used for functional switching.
Note: Table 537.4 of BS 7671:2018 permits the use of circuit-breakers for functional switching
purposes but, in each case, the manufacturer should be consulted to establish suitability.
537.4 5.5 Firefighter's switch
537.4.2 A firefighter's switch must be provided to disconnect the supply to any exterior electrical
installation operating at a voltage exceeding low voltage, for example, a neon sign or any
interior discharge lighting installation operating at a voltage exceeding low voltage.
Note: Such installations are outside the scope of this Guide; see Regulations 537.4.2 to 537.4.4 of BS
7671:2018.
On-Site Guide 55

5
56 On-Site Guide

The following durable labels are to be securelyfixed on or adjacentto installed equipment.
6.1 Retention of a dangerous electrical charge
416.2.5 If, behind a barrier or within an enclosure, an item of equipment such as a capacitor is
462.4 installed which may retain a dangerous electrical charge after it has been switched off,
a warning label must be provided. Small capacitors such as those used for arc extinction
and for delaying the response of relays, etc., are not considered dangerous.
514.1.1
514.10.1
Note: Unintentional contact is not considered dangerous if the voltage resulting from static charge
falls below 120 V DC in less than 5 s after disconnection from the power supply.
6.2 Where the operator cannot observe the
operation of switchgear and controlgear
Except where there is no possibility of confusion, a label or other suitable means of
identification must be provided to indicate the purpose of each item of switchgear
and controlgear. Where the operator cannot observe the operation of switchgear and
controlgear and where this might lead to danger, a suitable indicator complying, where
applicable, with BS EN 60073 and BS EN 60447, should be fixed in a position visible to
the operator.
6.3 Unexpected presence of nominal voltage
exceeding 230 V
Where a nominal voltage exceeding 230 V to earth exists and it would not normally be
expected, a warning label stating the maximum voltage present must be provided where
it can be seen before gaining access to live parts.
Note that a TN/TT, i.e. earthed neutral, three-phase system with 400 V between line
conductors will have nominal voltage of 230 V to earth, therefore, a warning notice will
not be required for such systems.
On-Site Guide 57
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6
514.13.1
514.1.1
514.8.1
6.4 Earthing and bonding connections
A permanent label to BS 951 (Figure 6.4) must be permanently fixed in avisible position
at or near the point of connection of:
(a) every earthing conductor to an earth electrode,
(b) every protective bonding conductor to extraneous-conductive-parts, and
(c) at the main earth terminal, where it is not part of the main switchgear.
T Figure 6.4 Label at connection of earthing and bonding conductors
6.5 Purpose of switchgear and controlgear
Unless there is no possibility of confusion, a label indicating the purpose of each item of
switchgear and controlgear must be fixed on or adjacent to the gear. It may be necessary
to label the item controlled, in addition to its controlgear.
6.6 Identification of protective devices
A protective device, for example, afuse or circuit-breaker, must be arranged and identified
so that the circuit protected may be easily recognised.
6.7 Identification of isolators
537.2.7 Where it is not immediately apparent, all isolating devices must be clearly identified
by position or durable marking. The location of each disconnector or isolator must be
indicated unless there is no possibility of confusion.
514.11.1
58
6.8 Isolation requiring more than one device
A durable warning notice must be permanently fixed in a clearly visible position to
identify the appropriate isolating devices, where equipment or an enclosure contains live
parts which cannot be isolated by a single device.
On-Site Guide

514.12.1
514.9.1
6
6.9 Periodic inspection and testing
A notice of durable material indelibly marked with the words as Figure 6.9 must be fixed
in a prominent position at or near the origin of every installation. The person carrying
out the initial verification must complete the notice and it must be updated after each
periodic inspection.
'Y Figure 6.9 Label for periodic inspection and testing
IMPORTANT
This installation should be periodically inspected and tested and
a report on its condition obtained, as prescribed in the lETWiring
Regulations BS 7671Requirements for Electrical Installations.
Date of last inspection ............................................
Recommended date of next inspection ............................................
6.10 Diagrams
A diagram, chart or schedule must be provided indicating:
(a) the number of points, size and type of cables for each circuit,
(b) the method of providing protection against electric shock,
(c) information to identify devices for protection, isolation and switching, and
(d) any circuit or equipment vulnerable during atypical test, e.g. SELV power supply
units of lighting circuits which could be damaged by an insulation test.
For simple installations, the foregoing information may be given in a schedule, with a
durable copy provided within or adjacent to the distribution board or consumer unit.
On-Site Guide 59

6
514.12.2
514.14.1
6.11 Residual current devices
Where an installation incorporates an RCD, a notice with the words in Figure 6.11 (and
no smaller than the example shown in BS 7671:2018) must be fixed in a permanent
position at or near the origin of the installation.
T Figure 6.11 Label for the testing of a residual current device
This installation, or part of it, is protected by a device
which automatically switches off the power supply if an
earth fault develops. Test six-monthly by pressing the
button marked 'T' or 'Test'. The device should switch
offthe supply and should be then switched on to
restore the supply. If the device does not switch off the
supply when the button is pressed seek expert advice.
6.12 Warning notice - non-standard colours
If additions or alterations are made to an installation so that some of the wiring complies
with the harmonized colours of Table K1 in Appendix K and there is also wiring in the
earlier colours, a warning notice must be affixed at or near the appropriate distribution
board with the wording in Figure 6.12.
T Figure 6.12 Label advising of wiring colours to two versions of BS 7671
CAUTION
Thisinstallation has wiring colours to
two versions of BS 7671.
Great care should be taken before
undertaking extension, alteration or repair
that all conductors are correctly identified.
60 On-Site Guide

514.15.1
543.7.1.205
6
6.13 Warning notice - alternative supplies
Where an installation includes additional or alternative supplies, such as a PV installation,
which is used as an additional source of supply in parallel with another source, normally
the distributor's supply, warning notices must be affixed at the following locations in the
installation:
(a) at the origin of the installation
(b) at the meter position, if remote from the origin
(c) at the consumer unit or distribution board to which the additional or alternative
supply is connected
(d) at all points of isolation of all sources of supply.
The warning notice must have the wording in Figure 6.13.
T Figure 6.13 Label advising of multiple supplies
WARNING
MULTIPLE SUPPLIES
ISOLATE ALL ELECTRICAL SUPPLIES
BEFORE CARRYING OUT WORK
r-------------------~
ISOLATE MAINS AT
~------r=======~
ISOLATE ALTERNATIVE SUPPLIES AT
6.14 Warning notice - high protective conductor
current
At the distribution board, information must be provided indicating those circuits having
a high protective conductor current. This information must be positioned so as to be
visible to a person who is modifying or extending the circuit (Figure 6.14).
On-Site Guide 61

6
T Figure 6.14 Label advising of high protective conductor current
WARNING
HIGH PROTECTIVE CONDUCTOR
CURRENT
The following circuits have a high protective
conductor current:
. . . . . . . . . . . . 0 . . 0 . . 0 . . 0 • 0 0 • 0 • • 0 • • 0 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 0 •• 0
0 o o o o I o o o o o I o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o I o o o o o I o o o o o 0 o o o o 0 o o o o o 0 o + o o
6.15 Warning notice - photovoltaic systems
712.537.2 All junction boxes (PV generator and PV array boxes) must carry a warning label
indicating that parts inside the boxes may still be live after isolation from the PV convertor
(Figure 6.15).
T Figure 6.15 Label advising of live parts within enclosures in a PV system
62 On-Site Guide
WARNING
PVSYSTEM
Parts inside this box or enclosure may still
be live after isolation from the supply.

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